A feasibility study of functional preservation in craniospinal irradiation with photon for pediatric medulloblastoma

BACKGROUND: Craniospinal irradiation (CSI) is essential for treating pediatric medulloblastoma (MB) but causes significant long-term toxicities. Existing dose-reduction or partial-sparing strategies improve neurocognitive outcomes but may compromise survival or fail to address other late effects. METHODS: A new functional preservation CSI (FP-CSI) technique was developed to spare the hippocampus, hypothalamic-pituitary axis (HPA), cochlea, and scalp while ensuring homogeneous vertebral coverage. Eight pediatric patients with average-risk MB were retrospectively planned with volumetric modulated arc therapy (VMAT) using both FP-CSI and standard CSI (S-CSI). Dosimetric parameters for the planning target volume (PTV) and organs at risk (OARs), radiobiological effects, plan robustness, plan complexity, and plan quality assurance (QA) were compared. RESULTS: FP-CSI significantly reduced mean doses to the hippocampus (12.4 vs. 23.9 Gy), hypothalamus (14.7 vs. 23.9 Gy), and pituitary gland (15.4 vs. 24.1 Gy, all p < 0.01). Vertebral dose gradients were halved (4.7 vs. 8.7 Gy). Moderate dose reductions were also achieved for the cochlea and scalp. Compared with S-CSI, FP-CSI exhibited slightly inferior PTV homogeneity (HI: 0.16 vs. 0.07) and conformity (CI: 0.88 vs. 0.93), but coverage remained clinically acceptable. Normal tissue complication probability (NTCP) modeling showed pronounced decreases in predicted neurocognitive and endocrine toxicity risks, with probability of neurocognitive impairment reduced from 84.5% to 24.9% and probability of endocrine dysfunction from 44.7% to 27.3%. FP-CSI increased modulation complexity and produced slightly lower gamma passing rates for cranial beams, while spinal beam deliverability remained similar to S-CSI. Robustness analysis indicated greater sensitivity of FP-CSI to setup and rotational errors. Nevertheless, 3D dose reconstruction confirmed accurate delivery, with volumetric dose deviations generally below 1 Gy. CONCLUSION: FP-CSI effectively spares critical functional structures while maintaining clinically acceptable target coverage, and offers a promising strategy to reduce long-term radiotherapy-induced toxicities in pediatric MB.